linux-kernel - Re: [RFC][PATCH 2/2] printk: take console_sem when accessing console drivers list

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Date:   Thu, 25 Apr 2019 15:47:41 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [RFC][PATCH 2/2] printk: take console_sem when accessing console
 drivers list

On (04/25/19 14:19), Sergey Senozhatsky wrote:
> 
> So may be we can move the whole thing under console_sem.
> 

Something like below. I'll re-spin the series in a day or two,
we have time.

---
 kernel/printk/printk.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 52d1123d9fdc..0c2eb161e793 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2666,7 +2666,7 @@ static int __unregister_console(struct console *console)
  *  - Once a "real" console is registered, any attempt to register a
  *    bootconsoles will be rejected
  */
-void register_console(struct console *newcon)
+static void __register_console(struct console *newcon)
 {
 	int i;
 	unsigned long flags;
@@ -2771,7 +2771,6 @@ void register_console(struct console *newcon)
 	 *	Put this console in the list - keep the
 	 *	preferred driver at the head of the list.
 	 */
-	console_lock();
 	if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
 		newcon->next = console_drivers;
 		console_drivers = newcon;
@@ -2820,19 +2819,25 @@ void register_console(struct console *newcon)
 
 	console_unlock();
 	console_sysfs_notify();
+	console_lock();
 
 	if (keep_bootcon)
 		return;
 
 	if (bcon && (newcon->flags & (CON_CONSDEV|CON_BOOT)) == CON_CONSDEV) {
-		console_lock();
 		for_each_console(bcon)
 			if (bcon->flags & CON_BOOT)
 				__unregister_console(bcon);
-		console_unlock();
-		console_sysfs_notify();
 	}
 }
+
+void register_console(struct console *newcon)
+{
+	console_lock();
+	__register_console(newcon);
+	console_unlock();
+	console_sysfs_notify();
+}
 EXPORT_SYMBOL(register_console);
 
 int unregister_console(struct console *console)
-- 
2.21.0